1. Field of the Invention
The invention relates to an electrically conductive composition, and more particularly to an electrically conductive composition formed at a low temperature and a fabrication method thereof.
2. Description of the Related Art
Flexible electronic technology offers product design flexibility. The substrates and materials used for the flexible electronic technology need to be flexible. Considering the temperatures at which the flexible electronic technology fabrication processes and the flexible substrates and various flexible passive and active components can suffer, and the requirements for the flexible electronic technology of quick fabrication processes and low cost products, the flexible electronic materials need to be selected from materials that can be printed and fabricated at low temperatures.
Generally, conventional high conductivity materials used for printing are conductive metal ink, which is a conductive coating formed by high temperature sintering. Conventional conductive metal ink is usually used for rigid ceramic substrates. The other conductivity materials used for printing are polymer system metal ink which using in polymer substrate for low process temperature. The conventional conductive metal ink comprises an organic polymer, conductive metal particles and glass. In addition, a low temperature cured conductive epoxy resin or other thermosetting plastic are usually used for conventional flexible electronic materials. For high conductivity, the conventional flexible electronic conductivity materials are formed from a base curing material of polymer and an additive of sheet-shaped or high package densification conductive metal particles therein. Although the conventional flexible electronic material can be made at a temperature below 200° C., the conductivity thereof is too low and the polymer type conventional flexible electronic material is not solderable. Besides, the adhesion strength and the conductivity of the conventional flexible electronic material are easy to reduce at the high temperature of the subsequent processes.
The forming methods of the conductive metal ink are usually performed by using an additional energy to satisfy the requirements for a conductive film. Generally, the additional energy is provided from a thermal energy source to sinter the metal particles or to cure thermal cured resin for forming the conductive film. A part of the thermal energy source is taken by thermal radiation to implement energy delivery, for example taken by infrared rays, far-infrared rays or halogen lights to perform thermal radiation heating. Besides, using energy to excite molecules or atoms, or changing the energy level of the materials to produce energy, for example using a microwave heating or a laser heating methods also can achieve the effect of heating.
U.S. Pat. No. 7,026,432 discloses a high conductive ink formed from a polymer containing a metal atom and a single-walled nanometer scale carbon tube mixed with the polymer. The polymer or a polymer precursor thereof contains polyarylene ether resin, carbonyl compounds of polycarbonate, polyester or polyamide.
U.S. Pat. No. 7,062,848 discloses a printing material formed by adding purified nanometer scale materials to a liquid carrier. The nanometer scale materials in the liquid carrier have an aspect ratio of 5:1.
U.S. Pat. No. 7,060,241 discloses a transparent conductive film formed by mixing a polymer with a single-walled nanometer scale carbon tube or a dual-walled nanometer scale carbon tube. In this transparent conductive film, the single-walled nanometer scale carbon tube or the dual-walled nanometer scale carbon tube is dispersed by a small molecule dispersing agent. The polymer contains a thermal plastic resin, a thermal setting resin, elastomers and a conductive polymer.
International Patent No. WO 2008/045109A2 discloses an electromagnetic isolation material formed by mixing a nanometer scale material with a polymer. In this electromagnetic isolation material, the polymer is foamed polystyrene and the nanometer scale material is a nanometer scale carbon tube or other nanometer scale material. Moreover, a slight concentration dispersing agent is added into the electromagnetic isolation material to disperse the nanometer scale material.
Bakes, E. L. O. and Tielens, A. G. G. M. Et al. in Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 427, no. 2, p. 822-838 disclose a partial nanometer scale radiative heat transfer (RHT) produced between nanometer scale particles due to quantum effect there between.
Moreover, H. R. Astorga et al. in Optical Materials 27 (2005) 1228-1230 disclose nanometer scale material, for example a nanometer scale carbon tube has high electrical conductive ability and high thermal conductive ability. Liyue Liu and Yafei Zhang et al. in Sensors and Actuators A 116 (2004) 394-397 disclose nanometer scale carbon tubes and nanometer scale zinc oxide tubes have an absorption ability for a specific wavelength. A multi-walled nanometer scale carbon tube can be used for a new infrared light detection material. Meanwhile, nanometer scale carbon tubes have an electrical-photo character and are also useful electronic and thermal conductive material.
N. R. Bieri, J. Chung et al. at the year of 2003, in Applied Physics Letters, V82, No. 20, page 3529 disclose using a laser lighting method to sinter a gold nanometer scale particle ink, wherein the gold nanometer scale particle has a diameter of 10-100 nm. Because a nanometer scale particle with a diameter of 5 nm has an absorption ability for light of a wavelength greater than 0.6 μm, the sintering temperature for the gold nanometer scale particles can be reduced and a well conductivity thereof about 1.4×10−7 Ωm can be achieved. However, the above mentioned papers and patents only use a single energy source to implement the ink sintering.